Straw production and grain yield relationships in winter wheat

Winter wheat (Triticum aestivum L.) -fallow is the predominant cropping sys tem in low-precipitation regions (< 250 mm annually) of the inland Pacific Northwest (PNW) in the USA. Wind erosion is a recurrent problem during and after fellow periods when inadequate crop residue amounts are retained on t he soil surface. Management options that optimize both grain yield and stra w production are needed. A 3-yr held study was conducted to determine sowin g rate and sowing date effects on straw and grain yield, and grain yield co mponents of winter wheat cultivars with semidwarf, standard height, or tall growth habit. Four winter wheat cultivars were evaluated at three sowing r ates (65, 130, and 195 seeds m(-2)) and three sowing dates in August, Septe mber, and October. A split plot design was used, with sowing dates as main plots and sowing rate x cultivar combinations as subplots, The greatest eff ect of sowing date was on straw production. Straw biomass from mid-August s owing averaged 6.70 Mg ha(-1) compared with 4.65 and 2.78 Mg ha(-1) from mi d-September and mid-October sowing, respectively. Grain yield was highest f or mid-August sowing during two years and lowest for mid-October sowing all years. Averaged across years, the semidwarf cultivar produced the highest grain yield on all sowing dates and was equal to the standard height and ta ll cultivars for straw production. Path coefficient analysis showed that va riation in grain yield was due primarily to differences in spikes per unit area (SPU) and kernels per spike (KPS), Late sowing resulted in a large red uction in SPU and, therefore, grain yield. For cropland susceptible to wind erosion in east-central Washington, early sowing results in increased whea t straw production and generally higher grain yield compared with mid-to-la te sowing dates.